<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            padding: 0px;margin: 0px;
        }
        div{
            width: 10rem;
            height: 10px;border: 1px solid red;
        }
    </style>
    <script src="../js/flexible.js"></script>
</head>
<body>
    <div class="banner"></div>
</body>
<script>
    let bannerEl = document.querySelector('.banner');
    console.log('bannerEl.offsetWidth:' + bannerEl.offsetWidth);
</script>
</html>